1. Field of the Invention
The present invention relates to a light quantity controller for providing a stabilized light source and an input device for inputting a plurality of input signals to a controller.
2. Description of the Prior Art
In a copying machine, an image of a text is exposed by a light source in the machine to form a copy of the text.
A halogen lamp or a fluorescent lamp has been widely used as the light source, but the halogen lamp has defects in that it has a poor conversion efficiency, generates much heat which raises the temperature of the machine and adversely affects the components of the machine, and has a high power consumption. The fluorescent lamp has a defect in that a light quantity varies with a surrounding temperature (temperature of a tube wall of the fluorescent lamp). In the copying machine, the effect of the defects of the light source to the tone of the copy is substantial, as described above.
An approach to stabilize the light quantity of the light source has been proposed. In the proposed approach, the amount of energization of the light source is increased when the light quantity decreases so that the light quantity is increased to a desired level. The proposed approach also operates when the change in the light quantity is caused not by the phenomenon described above but by the degradation of the light source per se. Accordingly, if the degradation of the light source is such that the desired light quantity is not attained by increasing the amount of energization, power is wasted and the machine may be overheated by an excess current, which may lead to fire. As performance of a microcomputer is improved and the size thereof is reduced, various controls are carried out by the microcomputer. However, since the number of input/output ports of the microcomputer is limited, if a number of input signals are to be used as control information, a multiplexor or a key matrix circuit is usually used to process a large amount of control information with a small number of input ports.
FIG. 1 shows a control circuit which uses an input device having a key matrix circuit. Numeral 10 denotes a control unit having a microcomputer, O1-O4 denote output ports, I1-I4 denote input ports, R denotes a resistor, and M1-M16 denote switches arranged between the input ports and the output ports which constitute the key matrix circuit. An operator actuates one of the switches M1-M16 to enter control information. The control unit 1 produces time-divided repetitive pulse HIGH signals at the output ports O1-O4, detects which one of the input ports I1-I4 a HIGH signal is applied to, determines the actuated switch and reads a status of the key into a memory. With such a key matrix circuit, a maximum number of switches that can be arranged is m.times.n where m is the number of output ports and n is the number of input ports. Thus, only m.times.n control information can be processed. When the multiplexor is used, the input and output ports can be saved but the cost increases.